A magnetic resonance imaging apparatus (MRI apparatus) is an apparatus that images internal information of a subject by using a nuclear magnetic resonance phenomenon. An MRI apparatus acquires, with a coil, data referred to as k-space data by sampling nuclear magnetic resonance signals (MR signals) from certain atomic nuclei (e.g., atomic nuclei of hydrogen atoms) in the subject and acquires an MR image by applying the Fourier transform to the k-space data.
The MR signals are sampled as one-dimensional data. In order to acquire a two-dimensional MR image or a three-dimensional MR image, the MRI apparatus repeatedly performs one-dimensional sampling in a k-space, thereby acquiring necessary data for generating MR images. When a k-space data is sampled at the same resolution (full sampling) as that of an output MR image, by applying the Fourier transform to the acquired k-space data, generation of an MR image becomes possible. Furthermore, acquiring time-series images makes it possible to observe the motion of the subject.
There are two types of images that are generated by an MRI apparatus: magnitude images and phase images. Phase images are used to image the flow velocity. For example, in phase contrast MR angiography, time-series magnitude images and time-series phase images are output.
When k-space data is acquired and MR images are reconstructed, noise may be caused. As a method of removing the noise components to improve the image quality, there is a method using a filter.